Axial magnet assisted radial magnet air return motor for electromagnetic transducer

Abstract

An electromagnetic transducer such as an audio speaker, having an air-return motor. The use of an air return geometry lacking motor components in the region outside the voice coil assembly permits the spider and cone to be coupled to the bobbin much lower, significantly reducing the thickness of the transducer. The use of both a radially-charged primary magnet and axially-charged concentrating magnets provides greatly increased magnetic flux in the voice coil region. The primary magnet may be a cylindrical magnet or it may include a plurality of flat magnet segments arranged in a polygon. The motor may be coupled to the frame by steel bolts which pass through holes in the spider, to reduce the reluctance of the magnetic circuit.

1 . An electromagnetic transducer comprising: 
 (a) a frame;    (b) an air return motor coupled to the frame and including, 
 a radially-charged primary magnet having a first polarity oriented toward an outer surface of the primary magnet,  
 a first axially-charged concentrating magnet adjacent an end of the primary magnet and having the first polarity oriented toward the primary magnet; and  
   (c) a diaphragm assembly including, 
 a diaphragm,  
 an upper suspension component coupling the diaphragm to the frame,  
 a bobbin coupled to the diaphragm and extending over the motor, and  
 a voice coil coupled to the bobbin and disposed adjacent the outer surface of the primary magnet.  
   
     
     
         2 . The electromagnetic transducer of  claim 1  wherein the motor further includes: 
 a magnetically conductive focusing ring having an inner surface disposed adjacent the outer surface of the primary magnet;    wherein the voice coil is disposed adjacent an outer surface of the focusing ring.    
     
     
         3 . The electromagnetic transducer of  claim 2  wherein: 
 the outer surface of the focusing ring has a shape tapered inward at its ends.    
     
     
         4 . The electromagnetic transducer of  claim 1  wherein the motor further includes: 
 a second axially-charged concentrating magnet adjacent an opposite end of the primary magnet and having the first polarity oriented toward the primary magnet.    
     
     
         5 . The electromagnetic transducer of  claim 4  wherein the motor further includes: 
 a magnetically conductive focusing ring having an inner surface disposed adjacent the outer surface of the primary magnet;    wherein the voice coil is disposed adjacent an outer surface of the focusing ring.    
     
     
         6 . The electromagnetic transducer of  claim 5  further comprising: 
 a magnetically conductive core having an outer surface disposed adjacent an inner surface of the primary magnet.    
     
     
         7 . The electromagnetic transducer of  claim 1  further comprising: 
 a magnetically conductive core having an outer surface disposed adjacent an inner surface of the primary magnet.    
     
     
         8 . The electromagnetic transducer of  claim 1  further comprising: 
 a lower suspension component coupled to a lower end of the bobbin below the voice coil.    
     
     
         9 . The electromagnetic transducer of  claim 1  further comprising: 
 a plurality of magnetically conductive rods disposed at a corresponding plurality of positions about the motor, each extending substantially axially and substantially a length of the motor.    
     
     
         10 . The electromagnetic transducer of  claim 9  further comprising: 
 a cap disposed adjacent an upper end of the motor;    wherein the rods comprise bolts coupling the cap to the frame.    
     
     
         11 . The electromagnetic transducer of  claim 9  wherein: 
 the cap comprises a magnetically conductive end plate.    
     
     
         12 . The electromagnetic transducer of  claim 9  further comprising: 
 a lower suspension component coupled to the frame and to one of the bobbin and the diaphragm;    wherein the lower suspension component is adapted with holes through which the rods pass.    
     
     
         13 . The electromagnetic transducer of  claim 12  wherein: 
 the lower suspension component is coupled to a lower end of the bobbin below the voice coil.    
     
     
         14 . The electromagnetic transducer of  claim 1  wherein: 
 the air return motor further includes a magnetically conductive focusing ring having a polygonal inner surface; and    the primary magnet comprises a plurality of flat magnet segments each magnetically coupled to a respective face of the polygonal inner surface of the focusing ring.    
     
     
         15 . The electromagnetic transducer of  claim 14  wherein the air return motor further comprises: 
 a magnetically conductive inner core having a polygonal outer surface, faces of which are magnetically coupled to respective ones of the plurality of flat magnet segments.    
     
     
         16 . An electromagnetic transducer comprising: 
 (a) a frame;    (b) a motor including, 
 a radially-charged primary magnet,  
 a steel focusing ring disposed about an outer surface of the primary magnet,  
 a lower axially-charged concentrating magnet coupled to a lower end of the primary magnet and of the focusing ring, and  
 an upper axially-charged concentrating magnet coupled to an upper end of the primary magnet and of the focusing ring,  
 wherein the primary magnet, the lower concentrating magnet, and the upper concentrating magnet all have a same pole oriented toward the focusing ring; and  
   (c) a diaphragm assembly including, 
 a diaphragm,  
 a surround coupling the diaphragm to the frame,  
 a bobbin coupled to the diaphragm, and  
 an underhung voice coil coupled to the bobbin and disposed adjacent an outer surface of the focusing ring.  
   
     
     
         17 . The electromagnetic transducer of  claim 16  wherein the diaphragm assembly further comprises: 
 a spider coupled to the frame and coupled to one of the bobbin and the diaphragm substantially adjacent the voice coil.    
     
     
         18 . The electromagnetic transducer of  claim 17  wherein the motor further comprises: 
 a steel end plate coupled to the upper concentrating magnet opposite the primary magnet.    
     
     
         19 . The electromagnetic transducer of  claim 18  wherein the motor further comprises: 
 a steel end plate coupled to the lower concentrating magnet opposite the primary magnet.    
     
     
         20 . The electromagnetic transducer of  claim 18  wherein the frame comprises: 
 a steel frame;    and wherein the lower concentrating magnet is coupled to the steel frame.    
     
     
         21 . The electromagnetic transducer of  claim 16  wherein: 
 the outer surface of the focusing ring is tapered inward at its ends.